1. Field of the Invention
The present invention relates to a shadow mask in a cathode ray tube, and more particularly, to a shadow mask in a color cathode ray tube having an open type bridge no electron beam passes therethrough.
2. Background of the Related Art
As well known, the color cathode ray tube, one of electronic tubes, is a display used the most widely in many fields, starting from TV receivers and computer monitors to oscilloscopes and radar observation, and the like. The color cathode ray tube is called three color cathode ray tube, because a principle in which red, green, and blue colors are added together to reproduce a variety of colors. That is, three color fluorescent materials and three cathodes are used, and electron beams of electrons emitted from the cathodes are made to land on a screen having the three fluorescent materials coated thereon, for displaying a picture on the screen.
An exemplary related art color cathode ray tube having the shadow mask shown in FIGS. 1-3 employed therein will be explained. FIG. 1 illustrates a related art color cathode ray tube having a tension shadow mask schematically, FIG. 2 illustrates a plan view of a shadow mask, and FIG. 3 illustrates a section across a line Bxe2x80x94B showing slots and an open type bridge of a shadow mask.
Referring to FIG. 1, the color cathode ray tube is provided with a substantially rectangular panel 1, a funnel 4 of a funnel shape fitted to the panel 2, an in-line type electron gun 10 having a cylindrical neck 6 fitted continuous to a small diametered end of the funnel 4 to form an outer appearance thereof, for emitting the electron beams 8. A bonding force of the panel 2 and the funnel 4 is enhanced by a reinforcing band 12, a fluorescent screen 13 having the three color fluorescent materials of emitting red, green, and blue lights respectively is provided on an inside surface of the panel 2, and the shadow mask 20 supported on a frame 16 fitted to the panel 2 through springs 14 is provided with a gap from the fluorescent screen 13. There is a deflection yoke 18 on an outer circumference of the funnel 4 in the vicinity of the neck 6, for producing a pin-cushion type horizontal magnetic field, and a barrel type vertical magnetic field, to deflect the electron beams 8 to all of the surface of the fluorescent screen 13, and an inner shield 19 fixed to the frame 16 for shielding the electron beams 8 from external geomagnetism enclosed under a high vacuum. Particularly, as shown in FIG. 2, the shadow mask 20 welded to the frame 16 on the inside surface of the panel 2 has a plurality of slots 22, forming openings, formed at fixed intervals in horizontal and vertical directions, and a bridge 24 between adjacent vertical slots 22.
Under this state, the electron beams 8 from the electron gun 10 is deflected at a large angle by the vertical and horizontal deflection magnetic field, and the deflected electron beams 8 are converged onto the plurality of slots 22 in the shadow mask 20. When the electron beams 13, color selected as the electron beams 13 pass through the slots 22, land onto the fluorescent screen 13, the three color fluorescent materials emit lights, to reproduce a color picture on the panel 2.
FIG. 3 illustrates a partial section of the shadow mask 20 showing the slots 22 and the open type bridges 24. The open type bridge 24 is formed by removing a portion of the bridge to make the bridge discontinuous.
As can be known from the section, the slot 22 for passing the electron beams has a tapered form inclusive of an inlet 222 for receiving the electron beams 8 from the electron gun 10, and an outlet 224 for letting the electron beams 8 to leave for the fluorescent screen 13, which is formed to have a greater area than the inlet 222, wherein a difference STi of horizontal distances of an inlet edge 222a and an outlet edge 224a of the slot 22, near to a vertical center line xe2x80x98lxe2x80x99 of the shadow mask 20, is smaller than a difference STo of horizontal distances the inlet edge 222b and the outlet edge 224b of the slot 22, far from the vertical center line xe2x80x98lxe2x80x99 of the shadow mask 20. The same is applicable to the open type bridge 24 wherein a difference xe2x80x98Tixe2x80x99 of horizontal distances of an inlet edge 242a and an outlet edge 244a of the open type bridge 24, near to a vertical center line xe2x80x98lxe2x80x99 of the shadow mask 20, is also smaller than a difference To of horizontal distances the inlet edge 242b and the outlet edge 244b of the open type bridge 24, far from the vertical center line xe2x80x98lxe2x80x99 of the shadow mask 20. Sections of the slot 22 or the open type bridge 24 are formed to prevent distortion of the electron beams. For prevention of distortion of the electron beams, it is required to design the To and the STo shown in FIG. 4 to meet the following.
Referring to FIG. 4, with regard to the shadow mask 20 with a curvature, when it is assumed that xe2x80x98txe2x80x99 denotes a thickness of the shadow mask 20, xe2x80x98xcex1xe2x80x99 denotes a deflection angle of the electron beams incident to the shadow mask 20, and xe2x80x98xcex2xe2x80x99 denotes an angle of a normal vector to a surface to an axis of the cathode ray tube, To or STo can be expressed as follows;
To(or STo)=txc3x97tan(xcex8), xcex8=xcex1xe2x88x92xcex2,
A minimum value of STo or To that causes no distortion of the electron beams passing through the slot 22 or the open type bridge 24 of the shadow mask 20 can be calculated by above equation. Recently, of quality characteristics of the cathode ray tube, enhancement of the luminance values highly. For enhancing the luminance, it is required to lengthen the slot 22 for adjusting a transmissivity of the electron beams.
However, though the shadow mask with short slots and many number of bridges causes no problem with respect to vision as no shadows of the bridges are seen on the screen, the shadow mask with long slots and small number of bridges deteriorates a picture quality as shadows of the bridges are seen on the screen in forms of lines.
Only one horizontal slot may be provided removing the bridges entirely for eliminating such shadows of the bridges, when strength of the shadow mask is too weak to handle the shadow mask, and susceptible to vibration caused by external impact.
Accordingly, the present invention is directed to a shadow mask in a color cathode ray tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a shadow mask in a color cathode ray tube, which can enhance luminance while open type bridges having an advantage over doming are maintained, and quality deterioration caused by bridge shadows in view coming from lengthened slots with a reduced number of bridges can be overcome.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the shadow mask in a color cathode ray tube includes a plurality of slots for passing electron beams, and an open type bridge having a portion removed therefrom and dividing into slots in a vertical direction, wherein a difference xe2x80x98Tixe2x80x99 of horizontal distances of an electron beam inlet edge and an electron beam outlet edge of the open type bridge formed near to a vertical center line xe2x80x98lxe2x80x99 of the shadow mask is equal to, or greater than a difference xe2x80x98Toxe2x80x99 of horizontal distances of an electron beam inlet edge and an electron beam outlet edge of the open type bridge formed far from a vertical center line xe2x80x98lxe2x80x99 of the shadow mask.
A difference xe2x80x98SToxe2x80x99 of horizontal distances of an electron beam inlet edge and an electron beam outlet edge of the slot formed far from a vertical center line xe2x80x98lxe2x80x99 of the shadow mask is equal to, or greater than a difference xe2x80x98STixe2x80x99 of horizontal distances of an electron beam inlet edge and an electron beam outlet edge of the slot formed near to a vertical center line xe2x80x98lxe2x80x99 of the shadow mask.
A maximum xe2x80x98Toxe2x80x99 value of the open type bridge meets the following equation.
Max(To)=txc3x97tan(xcex8),
Where, xcex8=xcex1xe2x88x92xcex2, xcex1=a deflection angle of the electron beams, t=a thickness of the shadow mask, and xcex2=an angle of a normal vector to a mask surface to a cathode ray tube axis.
In another aspect of the present invention, there is provided a shadow mask in a color cathode ray tube including a plurality of slots for passing electron beams, and an open type bridge having a portion removed therefrom and dividing into slots in a vertical direction, wherein an angle xe2x80x98xcexxe2x80x99 between a line connecting a center of the electron beam inlet and a center of the electron beam outlet of the open type bridge to a horizontal plane is not greater than a deflection angle xe2x80x98xcex1xe2x80x99 of the electron beams.
In further aspect of the present invention, there is a shadow mask in a color cathode ray tube including a plurality of slots for passing electron beams, and an open type bridge having a portion removed therefrom and dividing into slots in a vertical direction, wherein an amount of taper xe2x80x98Tixe2x80x99 formed at a location near to a vertical center line of the shadow mask is equal to, or greater than an amount xe2x80x98Toxe2x80x99 of taper formed at a location far from the vertical center line of the shadow mask.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.